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What happens in the event of an avalanche accident?

26.06.2023

The typical skier avalanche is around 50-70 meters wide and has about three times the flow length. The fracture depth (also known as the break-off height ) is around half a meter on average. Most people die in avalanches as a result of suffocation (approx. 57%) or fatal injuries (30%). As a general rule, the chances of survival decrease with increasing burial time.

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This article is about:

01

Possible consequences

You don’t have to die in an avalanche, and many avalanche accidents fortunately have a mild outcome, i.e. almost no consequences. However, freeriders often suffer serious or even life-threatening injuries. As soon as you are caught in an avalanche, you are a passenger and it is difficult to influence the outcome of this event.

It is therefore important to avoid an avalanche as far as possible and to always consider the consequences of an avalanche in the current situation (terrain traps, burial time, risk of injury, rescuing companions, flying weather, etc.).

Several components always come together in an avalanche accident:

  • The forces acting in avalanches are enormous (dry slab avalanches can reach speeds of up to 250/300 km/h). This means that even if you do not hit a tree or other obstacle and/or are not buried, you can suffer serious injuries during the descent due to the enormous masses and resulting forces.
  • Even if you survive an avalanche unharmed, equipment may be missing afterwards, making further descent impossible. In combination with a lack of cell phone connection, remote terrain, no flying weather, darkness falling, etc., this can quickly lead to a serious emergency situation.
  • If a freerider is traveling alone or separated from the other group members, even a partial burial, where the head and upper body are free, can mean that you can no longer free yourself from the snow. Good communication within the group (cell phone, radio) and the buddy principle (groups of two who look out for each other) pay off here.
  • In the case of a non-visible complete burial (entire body buried in snow), time is running out. In order to maintain the chances of survival, the head (independent breathing) or the whole body (no breathing) must be uncovered in the first 15 minutes. In open terrain, only the partners on site can help during this time, and they must have the appropriate equipment and skills.
Cause of death of all avalanche victims, source: ÖKAS © snow institute
Cause of death of avalanche victims, source: ÖKAS © snow institute

This is why time – until the brain can be supplied with oxygen again – plays such an important role in an avalanche accident. Hypothermia, on the other hand, which is still frequently discussed, is of secondary importance, but can become an issue when waiting for the rescue services after being dug out(heat management!)

02

Survival curve

Survival curve according to Hermann Brugger et al. 2001 © snow institute

The “survival curve”, also known statistically as the “survival function”, shows the probability of still being alive in an avalanche over the course of a complete burial. It describes a gradual decrease in the probability of survival and allows the chances of survival during a complete burial to be divided into four phases:

Survival phase:

During the first 15 minutes (max. 18 minutes) after a burial, the probability of survival remains high at around 90 percent. During this phase, around ten percent of accident victims die, mainly from fatal injuries.

Asphyxiation phase:

This is followed by a steep descent. Approximately two thirds of all fully buried victims die from lack of oxygen in this phase.

Latency phase:

From 35 minutes, only completely buried people with a sufficient oxygen supply survive. They are able to breathe in the snow, so their airways are clear. At best, they have a sufficiently large breathing cavity. Only a few buried victims die during the latency phase. The survival function therefore shows a very flat curve from 35 to around 90 minutes.

From 90 minutes:

However, the chance of survival decreases again after the burial time (which roughly corresponds to the target time for an organized rescue). In this phase, three factors lead to death: severe hypothermia, lack of oxygen and an increase in carbon dioxide (due to the rebreathing of exhaled air).

In those cases in which buried persons have a so-called “breathing cavity”, i.e. a cavity in front of their mouth and nose or a connection to the outside air, it is even possible for them to survive a burial for several hours.

03

Conclusion

In summary, it can be said that only companion rescue offers a realistic chance of being rescued alive from the masses of snow. Avalanche airbags are a very useful addition to the standard emergency equipment (avalanche transceiver, shovel and probe), as they can prevent complete burial in many cases and make subsequent rescue easier.

04

Additional information on the survival curve

A comparative analysis of the survival curves from 2001 and 2005-2013 reveals some differences: The earlier survival curves were published based on Swiss data, and the 2001 data set was more extensive. In view of this, it made sense to compare the data with that of other countries in order to determine whether there are similarities or geographical differences.

In 2011, Pascal Haegeli, Markus Falk et al. compared the survival curve from Switzerland with that from Canada. This study showed that the four phases of survival probability differed slightly, which was due to local factors:

  • Due to a higher proportion of fatal injuries, particularly as a result of numerous avalanches in forested areas, the survival curve started lower in Canada.
  • The drop in the smothering phase also began earlier and was somewhat steeper, which can be attributed to higher snow density due to the proximity to the Pacific Ocean.
  • In addition, Canada showed a lower proportion of long-term survivors compared to Switzerland, which can be explained by the greater distances and the later onset of professional rescue operations.

Based on this investigation, the question arose as to whether there are differences in the survival curves between the individual Alpine countries that indicate possible climatic differences and whether there are differences in mountain rescue success. A comparison of the survival curve between Switzerland and Austria was therefore also carried out.

Data

This survival curve is based on a retrospective analysis of all avalanche accidents during the winter seasons from 2005/06 to 2012/13 in Austria and Switzerland. The data for Austria was taken from the Alpine Police database, while the data for Switzerland was taken from the avalanche register of the WSL Institute for Snow and Avalanche Research in Davos. Only accidents involving people who were completely buried and for whom comprehensive information was available were taken into account in the analysis. In total, the data of 633 completely buried avalanche victims were analyzed, with 333 victims in Austria and 300 victims in Switzerland.

This article is based on the following publications:

Haegeli P, Falk M, Brugger H, et al: Comparison of avalanche survival patterns in Canada and Switzerland. CMAJ 2011; 183: 789-95

Procter E, Brugger H, Falk M: Survival probability of avalanche burial

Procter E, Strapazzon G, Dal Cappello T, Zweifel B, Würtele A, Renner A, Falk M, Brugger H. Burial duration, depth and air pocket explain avalanche survival patterns in Austria and Switzerland. Resuscitation 2016; 105: 173-176.

Brugger, H., Durrer, B., Adler-Kastner, L., Falk, M., & Tschirky, F. (2001). Field management of avalanche victims. Resuscitation, 51(1), 7-15.

Cover picture: © snow institute | LWD Tirol

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